1. Field of the Invention
The present invention relates to semiconductor device and method for manufacturing the same by selectively forming a metal thin film on a semiconductor substrate as a contact plug.
2. Description of the Related Art
As the high integration and microminiaturization of a semiconductor device have recently been promoted, a multi-layer wiring technology becomes essential. In order to accomplish the multi-layer wiring structure, a device region of a MOS or bipolar transistor and the metal wire, or a Plurality of metal wires must be interconnected through an insulation film.
In the past, in order to conduct such wiring, a desired contact hole is formed in the insulation film and a metal wire is buried in the contact hole simultaneously with the formation of an upper layer metal wire. However, recently, a diameter of the contact hole is in the order of sub-micron and an aspect ratio of the contact hole formed in the insulation layer is larger than unity. The aspect ratio is defined as a ratio of a depth to a diameter of the opening. As the aspect ratio increases, the metal wire does not fully go into the contact hole and positive connection may not be attained.
In order to avoid the above problem, a tungsten selective growth method as disclosed in JP-A-4-25159 has been proposed.
The wiring formation method of the above patent application is briefly explained. First, an insulation film is formed on a semiconductor substrate and a contact hole is formed in the insulation film. A relatively thin metal silicide film is formed on an entire surface of a semiconductor substrate as a seed for selective growth and then a photo-resist film is formed on the semiconductor substrate, and then the photo-resist film and the metal silicide film are etched back to keep the metal silicide film only within the contact hole. After the photo-resist film remaining in the contact hole is removed, a tungsten film is selectively grown in the contact hole by using the metal silicide as the seed. Thus, a wiring layer including the tungsten film which is fully fills the contact hole is formed. Since the tungsten film is hard to be formed on the insulation film, the metal silicide film is formed as the seed for the selective growth.
However, in the method of the above patent publication, since the metal silicide film remains at the opening portion of the contact hole (an upper edge of the contact hole), when the tungsten film is selectively grown in the contact hole by using the metal silicide film as the seed and the contact hole is filled with the tungsten film, the tungsten film also grows from the opening portion of the contact hole and the tungsten film spreads out of the opening portion of the contact hole. As a result, when the metal wiring is formed on the tungsten film spread out of the opening portion of the contact hole, inferior wiring shape or inter-wiring short-circuit may occur.
JP-A-5-283536 discloses a manufacturing method which prevents titanium/titanium nitride on an inner wall of a contact hole from being etched by misalignment when a conductive film formed on the contact hole is etched to form the wiring.
This method is briefly explained. After the titanium/titanium nitride is sputtered on the inner wall of the contact hole formed in an interlayer insulation film on a semiconductor substrate, tungsten is vapor-grown to fill the contact hole. Then, the surface of the interlayer insulation film is exposed by dry etching and only the titanium/titanium nitride is selectively etched to form a groove. After a silicon oxide film is vapor-grown to fill the groove, the surface of the tungsten is exposed by dry etching and a conductive film is sputtered thereon. The conductive film is dry etched by using a photo-resist as a mask to complete the wiring.
In this method, however, an area of the contact is substantially reduced by the thickness of the silicon oxide film and a higher accuracy is required in positioning when the wiring is formed on the contact hole. On the other hand, if the contact hole is enlarged accordingly, it is against the high integration of the semiconductor device. Further, a process to vapor grow the silicon oxide and a process to expose the surface of the tungsten by the dry etching are required and it makes the manufacturing process of the semiconductor device complex.
It is an object of the present invention to provide semiconductor device and method for manufacturing the same which do not make a manufacturing process of the semiconductor device complex and do not cause inferior wiring shape or short-circuit of wiring when the semiconductor devices are highly integrated.
In order to achieve the above object, according to the present invention, the method for manufacturing a semiconductor device having an insulation film comprises the steps of forming a contact hole in the insulation film, forming a first conductive film on an entire surface including an inner surface of the contact hole, applying a film for filling the contact hole, etching the applied film until a distance from an opening portion of the contact hole to a surface of the applied film is not smaller than one-half of a width of the contact hole less twice of a thickness of the first conductive film while the applied film remains at a bottom of the contact hole, etching the first conductive film by using the applied film as a mask, removing the remaining applied film, and selectively growing a second conductive film to fill the contact hole by using the first conductive film remaining on the inner surface of the contact hole as a seed for the selective growth.
According to the present invention, the semiconductor device comprises a semiconductor substrate, an insulation film formed on said semiconductor substrate and having a contact hole, a first conductive film formed on an inner surface of said contact hole, a distance from an opening portion of said contact hole to an upper end of said first conductive film being not smaller than one-half of a width of said contact hole less twice of a thickness of said first conductive film and a second conductive film formed on said first conductive film to fill said contact hole.
In accordance with the present invention, in order to etch away the first conductive film (barrier layer) which serves as a seed for the selective growth of the second conductive film (plug) above the contact hole until a predetermined condition is met, the filling of the contact hole is completed before the second conductive film spreads out of the upper edge of the contact hole when the second conductive film is selectively grown in the contact hole.
When a plurality of contact holes of different widths are present, the first conductive film is etched away above the contact hole such that the predetermined condition is met for the widest contact hole. Thus, when the second conductive film is grown in the contact hole, the second conductive film does not spread out of the upper edge of any of the contact holes.
Further, since the first or second conductive film is fully filled in the contact hole, the entire area may be used as the contact and the high integration of the semiconductor device is not prevented.